Purification of branched chain paraffins



Patented Dec. 5, 1950 v-:PURIFIGATION F BRANCHED CHAIN PARAFFINS Alfred E. Hirschler, Drexel Hill, Pa., assignor :to

c Sun Oil Company, Philadelphia, -Pa a corporation of New Jersey No Drawing. Application May'27, 1946, Serial No. 672 686 "This ,invention relates to the separation of 'hydrocarbons and is particularly directed to a method of preparing I a branched c'hai-n paraffin ihydrocarbon of relatively high purityv from a mixture comprising the same together-with "one "or more naphthene hydrocarbons.

In the preparation of individual hydrocarbon "by organicsynthesis, it is seldom'thatthe desired hydrocarbon may be produced-directly in a highstate of purity. Generally-a mixture of hydrocarbons is formed, which includes compounds whichmay boil relatively close'to thedesired hydrocarbon. A usual procedureofpurification involves distillation under fractionatin-g conditions whereby removal of compounds havof the desired. hydrocarbon maybe accomplished.

It is often the case, however, that a highdegree of purity may not be attained "in this-manner, or may be obtained only with great difficulty, due to the proximity of boilingpoints 'of thevarious "compounds. Likewise, inthes epa-ration' ofaparticular hydrocarbon from a complex hydrocarbon mixture such as-petroleum or coal tar fractions, it is often extremely difficult-to segregate the desired component as a product of high purity due to the presence of other-compounds of close boiling points. While the use along-with straight distillation of other procedures, such as solvent extraction and azeotropic "distillation, has 'resulted in improved separations-in certain'cases, generally speaking it has'not been practical-here- -t0f0re to produce hydrocarbons of high purity from mixtures containing closely related hydrocarbons. Usually the best that has been-done;

from a practical aspect is to prepare hydrocarbons of'technical purity, such asi-n concentrations in the order of 80% -to95%. To produce hydrocarbons in a high state of purity, for 'ex- :ample, in concentrations better than 95%, from mixtures containing close boiling compounds heretofore has been extremely difiicult and, in many cases, practically impossible.

The present invention provides an improved method whereby relatively pure branched chain accomplished according to the invention by selective adsorption of the "naphthene iron; the branched chain paraflin, utilizing activated car;-

Juon as the .adsorbent. p

The removal of .a naphthenefromzaibranched chain paraffin hydrocarbon by selective adsorp-.;,;

"branched chain paraffinmaphthene tion 'of the parai'lin :on activated :carbon, '80 :as t obtain :theparaifiin in a relatively high state of purity, "does ..not::appear to have been accom' -plished heretofore. I haveiiound that activated carbon is capable of removing the naphthenil: component from some mixtures of this type-re- :gardless'of the :concentration of the parafin in the mixture. This is particularl true Where the parafiin :has a very highly branched chain. For example, 2,2,4-trimethylpentane-methylcyclohexane and 2,2-dimethylbutane-cyclohexane are mixtures .from :which activated carbon will selectivelyzremove the .naphthene substantially regardless .of the proportion ofnaphthene in the mixture.

I-have further found that there are many other mixtures from which. activated carbon will not selectively adsorb the naphthene when present in large proportion "but will, however, selectively remove the naphthenewhen its proportion'is not-too. great in the mixture. Paraflin's-which are not so'highly branched chain tend to form this'type of mixture. 'Whenthe behavior is of this'type, the parafiin may be purified by starting with'a mixture containing the naphthenic componentiin a proportion substantially less than that at which the paraffin is selectively adsorbable, for example, a

-mixture composed of more than of the paraflinitogethenwith only a small amount of the naphthene, and then treating such mixture with 'activated carbon. The smaller the amount of the naphthene the more easily its removal may :be efiected. This is in contrast to other separa ':tion methods such as distillation or solvent exis selected-which contains the naphthenic com ponentrin a proportion at which it is selectively dsorbable. Thechargashould contain a large vamount of the desired branched .chain paraffin and .only a'small amount (say 20% or less) of the-'naphthene as impurity. This mixture is then treated with activated carbon to selectively adsorb the naphthene. In order to effect a high degree of -.separation, this treatment is carried .ut preferably by percolating the charge through :a column of the adsorbent while employing a large proportion of the. adsorbent. After allof material mores-strongly adsorbable by activated carbon than the adsorbate in order to effect displacement of the charge material from the adsorbent. Examples of suitable desorbing agents are benzene, toluene, xylene, phenol or other aryl compounds. A relatively low boiling aliphatic hydrocarbon such as butane or pentane also may be employed as the desorbing agent, particularly when the charge material is sufiiciently high boiling to be readily separable therefrom by distillation. A desorbin agent is not required, however, if sufiicient charge is used to wet all of the adsorbent and produce a filtrate. The first portion of efliux or filtrate from the column will comprise the branched chain paraffin in a relatively high state of purity as compared to the charge. Succeeding portions will decrease in purity and, as the adsorbate is displaced from the gel, the filtrate will become less pure than the charge. The filtrate from the column may be out into fractions as desired in order to segregate the portion containing the parafiin in the purity desired. The following examples, in which percentages are by volume, will serve to illustrate more specifically how the invention may be practiced:

Example I A column having an internal diameter of about inch and a height of 3 feet was packed with 50 grams of 60-90 mesh activated carbon. The column was provided with a water jacket through which water was continuously circulated at a temperature of about 45-50 F. to absorb heat generated due to wetting of the adsorbent. Forty-nine milliliters of a starting mixture consisting of 89.5% 2,2,3-trixnethylbutane and 11.5% cyclohexane were percolated down through the column. After all of the charge had passed into the adsorbent, it was followed by benzene to displace the charge material from the column. The filtrate was collected in fractions and the composition of each fraction was determined. Results were as follows:

F f Contgent of w ractiono 2,2, -tri- Charge methylbutane Per cent Per cent It may be seen that the cyclohexane was selectively removed, resulting in a substantial purification of the 2,2,3-trimethylbutane. Still further purification could have been efiected by retreating the cuts with activated carbon.

Example II In this example a mixture consisting of 90% 2,2-dimethylbutane and 10% cyclohexane was treated in the same manner as described in Example I in order to purify the pa'rafiin component. The following results were obtained:

These results show that extremely pure 2,2- dimethylbutane may be made from the starting mixture according to the present method.

Example III This run was carried out in the same manner as in Example I with a starting mixture consist- In practicing the invention it generally will be desirable to reactivate the adsorbent after it has been used in order that it may be used again. This may be done by blowing the adsorbent with hot inert gas or air to drive off the adsorbed hydrocarbons or to drive off the desorbing agent if one has been used.

The temperature atwhich the adsorption operation is carried out may afiect the efficiency of the separation and it often will be the case that a poorer separation will be obtained at elevated temperature. The operation therefore is preferably conducted at room temperature or below to insure a better separation. This generally will necessitate the provision of some means for removing any heat generated due to wetting of the adsorbent as, for instance, by providing means for circulating a cooling medium around the adsorbent column.-

Various modifications of the herein described process are permissible within the broad aspects of the invention and will be apparent to those skilled in the art.

Having described my invention, what I claim and desire to protect by Letters Patent is:

1. A process for purifying a branched chain paraffin hydrocarbon from a liquid mixture composed of more than of said paraffin hydrocarbon together With a small amount of a naphthene hydrocarbon as impurity which comprises filtering the mixture through a body of activated carbon, thereby selectively adsorbing said naphthene, and separating from the activated carbon a filtrate fraction containing said branched chain parafiin hydrocarbon in more nearly pure form.

2. Process according to claim 1 wherein the said hydrocarbonsdiffer by not more than two carbon atoms per molecule.

3. Process according to claim 1 wherein the said hydrocarbons have the same number of carbon atoms per molecule.

ALFRED E. HIRSCHLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,306,610 Barrer Dec. 29, 1942 2,415,315 Walter et a1 Feb. 4, 1947 2,425,535 Hibshman Aug. 12, 1947 OTHER REFERENCES Mair et al., Jour. Res. Nat. Bur. of Stand, vol. 32, -183 (1944).

Mair et al., The Oil and Gas Journal, September 19, 1935, pages 29, 30 and 32. 

1. A PROCESS FOR PURIFYING A BRANCHED CHAIN PARAFFIN HYDROCARBON FROM A LIQUID MIXTURE COMPOSED OF MORE THAN 80% OF LSAID PARAFFIN HYDROCARBON TOGETHER WITH A SMALL AMOUNT OF NAPHTHENE HYDROCARBON AS IMPURITY WHICH COMPRISES FILTERING THE MIXTURE THROUGH A BODY OF ACTIVATED CARBON, THEREBY SELECTIVELY ABSORBING SAID NAPHTHENE, AND SEPARATING FROM THE ACTIVATED CARBON A FILTRATE FRACTION CONTAINING SAID BRANCHED CHAIN PARAFFIN HYDROCARBON IN MORE NEARLY PURE FORM. 